Head and neck squamous-cell cancer and its association with polymorphic enzymes of xenobiotic metabolism and repair

Tobacco smoking, alcohol drinking, and occupational exposures to polycyclic aromatic hydrocarbons are the major proven risk factors for human head and neck squamous-cell cancer (HNSCC). Major research focus on gene-environment interactions concerning HNSCC has been on genes encoding enzymes of metabolism for tobacco smoke constituents and repair enzymes. To investigate the role of genetically determined individual predispositions in enzymes of xenobiotic metabolism and in repair enzymes under the exogenous risk factor tobacco smoke in the carcinogenesis of HNSCC, we conducted a case-control study on 312 cases and 300 noncancer controls. We focused on the impact of 22 sequence variations in CYP1A1, CYP1B1, CYP2E1, ERCC2/XPD, GSTM1, GSTP1, GSTT1, NAT2, NQO1, and XRCC1. To assess relevant main and interactive effects of polymorphic genes on the susceptibility to HNSCC we used statistical models such as logic regression and a Bayesian version of logic regression. In subgroup analysis of nonsmokers, main effects in ERCC2 (Lys751Gln) C/C genotype and combined ERCC2 (Arg156Arg) C/A and A/A genotypes were predominant. When stratifying for smokers, the data revealed main effects on combined CYP1B1 (Leu432Val) C/G and G/G genotypes, followed by CYP1B1 (Leu432Val) G/G genotype and CYP2E1 (-70G>T) G/T genotype. When fitting logistic regression models including relevant main effects and interactions in smokers, we found relevant associations of CYP1B1 (Leu432Val) C/G genotype and CYP2E1 (-70G>T) G/T genotype (OR, 10.84; 95% CI, 1.64-71.53) as well as CYP1B1 (Leu432Val) G/G genotype and GSTM1 null/null genotype (OR, 11.79; 95% CI, 2.18-63.77) with HNSCC. The findings underline the relevance of genotypes of polymorphic CYP1B1 combined with exposures to tobacco smoke.

Elevated bladder cancer risk due to colorants--a statewide case-control study in North Rhine-Westphalia, Germany

Occupational exposure to aromatic amines is a known bladder cancer risk factor, whereas the impact of exposure to azo dyes, which may release aromatic amines in humans, is at present controversial. Therefore, the impact of occupational exposures to colorants was investigated in 156 bladder cancer cases and 336 controls in the state of North Rhine-Westphalia. All bladder cancer cases and controls (diagnosed with prostate cancer) requested after-care treatment. The subjects were investigated using a questionnaire for all occupations ever performed for more than 6 mo and for exposures to several possible occupational and nonoccupational bladder carcinogens. The relative bladder cancer risk was adjusted for age and smoking. The adjusted odds ratio (OR) for bladder cancer was elevated in 7 painters (OR 1.98, 95% CI 0.64-6.11), 4 hairdressers (OR 4.9, 95% CI 0.85-28.39), and 16 cases who reported a wood processing occupation (OR 1.19, 95% CI 0.58-2.41). Ten of these 16 cases reported chronic exposure to colorants (OR 1.84, 95% CI 0.68-4.95). The results of this epidemiological study confirm the hypothesis that individuals exposed to colorants show an elevated bladder cancer risk.

UDP-glucuronosyltransferase 2B7 C802T (His268Tyr) polymorphism in bladder cancer cases

A study of Chinese benzidine workers indicated elevated levels of UDP-glucuronosyltransferase (UGT) 2B7 T/T activity in carriers for development of bladder cancer. The present study was designed to investigate the possible impact of the presence of UGT2B7 genotype on bladder cancer risk in Caucasians. UGT2B7 polymorphism at locus C(802)T (His(268)Tyr) was detected using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based procedure. The study group consisted of 211 bladder cancer cases and 210 controls suffering from different urological diseases, but without any history of cancer. Both groups were recruited from a Department of Urology located in a center of former chemical and rubber industries in Germany. Furthermore, 171 bladder cancer cases with a history of occupational exposure to aromatic amines surveyed for compensation due to an occupational disease were investigated. T/T genotype frequencies in bladder cancer cases, urological controls, and exposed patients appeared similar (27 vs. 35 vs. 25%). This study indicated that there were ethnic differences between Caucasian and Chinese general populations with respect to the UGT2B7 genotype. Furthermore, in contrast to an earlier investigation in benzidine-exposed Chinese bladder cancer patients, no relevant differences between bladder cancer patients and urological hospital controls were observed in Germany.

Dephenylation of the rubber chemical N-phenyl-2-naphthylamine to carcinogenic 2-naphthylamine: a classical problem revisited

N-phenyl-2-naphthylamine (PBNA) represents an example of a suspected carcinogen that is found negative in mutagenicity and clastogenicity testing as well as in long-term animal carcinogenicity bioassays in several species, but for which a carcinogenic risk cannot be excluded because of its metabolic conversion to the known human carcinogen 2-naphthylamine. Also, epidemiologic studies failed to indicate an elevated bladder cancer risk in humans occupationally exposed to PBNA. The amounts of 2-naphthylamine found in the urine of different species including humans after exposure to PBNA indicate unequivocally that PBNA is dephenylated to some extent. These are not explained by the 2-naphthylamine impurities in technical-grade PBNA. To explain the metabolic dephenylation process, it has been suggested that PBNA is metabolized by cytochrome P-450 (CYP) enzymes to the phenolic derivative 4'-hydroxy-N-phenyl-2-naphthylamine, followed by its further oxidation to the quinone imine, which subsequently hydrolyses to form the dephenylation product 2-naphthylamine. Phenolic metabolites from the initial CYP-mediated activation step are rapidly conjugated. Quantitatively, dephenylation of PBNA to 2-naphthylamine is a minor pathway. The dog represents an animal model that appears to approximate the human metabolism and biological activation of PBNA. Based on published data, a worst-case scenario indicates that about 1% of total PBNA taken up is transferred into 2-naphthylamine. However, in vitro as well as in vivo findings with PBNA may point to a significantly smaller conversion rate, as metabolites anticipated from the metabolism of 2-naphthylamine were not detected so far. The assumption, which may well be an overestimation, is compatible with findings in animal experiments, and explains the lack of direct evidence of carcinogenicity of PBNA in both experimental and epidemiological studies.

Strategy of the scientific committee on occupational exposure limits (SCOEL) in the derivation of occupational exposure limits for carcinogens and mutagens

Setting standards, such as occupational exposure limits (OELs) for carcinogenic substances must consider modes of action. At the European Union level, the scientific committee on occupational exposure limits (SCOEL) has discussed a number of chemical carcinogens and has issued recommendations. For some carcinogens, health-based OELs were recommended, while quantitative assessments of carcinogenic risks were performed for others. For purposes of setting limits this led to the consideration of the following groups of carcinogens. (A) Non-threshold genotoxic carcinogens; for low-dose assessment of risk, the linear non-threshold (LNT) model appears appropriate. For these chemicals, regulations (risk management) may be based on the ALARA principle ("as low as reasonably achievable"), technical feasibility, and other socio-political considerations. (B) Genotoxic carcinogens, for which the existence of a threshold cannot be sufficiently supported at present. In these cases, the LNT model may be used as a default assumption, based on the scientific uncertainty. (C) Genotoxic carcinogens with a practical threshold, as supported by studies on mechanisms and/or toxicokinetics; health-based exposure limits may be based on an established NOAEL (no observed adverse effect level). (D) Non-genotoxic carcinogens and non-DNA-reactive carcinogens; for these compounds a true ("perfect") threshold is associated with a clearly founded NOAEL. The mechanisms shown by tumour promoters, spindle poisons, topoisomerase II poisons and hormones are typical examples of this category. Health-based OELs are derived for carcinogens of groups C and D, while a risk assessment is carried out for carcinogens of groups A and B. Substantial progress is currently being made in the incorporation of new types of mechanistic data into these regulatory procedures.

The debate on carcinogenicity of permanent hair dyes: new insights

Oxidative (permanent) hair dyes contain one or several "primary intermediates" (e.g., p-phenylenediamines, p-aminophenols) and "couplers" (e.g., m-aminophenols, m-hydroxyphenols). In the presence of peroxide, the primary intermediate(s) and the coupler(s) undergo a chemical reaction to form colored oligomers. In the 1970s a number of aromatic amines used in oxidative hair dyes were identified as mutagenic and/or carcinogenic in rodents after lifetime oral administration. In response, regulatory action was taken, and some hair dye ingredients were banned in the European Union. Although recent results suggest that the main "primary intermediate" of oxidative hair dyes, p-phenylenediamine, has a weak genotoxic potential in vitro, it was not mutagenic in a mixture with nonmutagenic couplers, if tested under conditions comparable to those of practical use. Under conditions of use of permanent hair dyes, between 0.1 and 0.5% of the applied p-phenylenediamine may be absorbed through the skin. Acetylation in the skin is a key metabolic step for the primary intermediates p-phenylenediamine and p-aminophenol. Because of the involvement of aromatic amines, the discussion on the carcinogenicity of hair dyes in humans has been focused on urothelial cancer. Numerous epidemiological studies have investigated the risk of bladder cancer associated with the profession as a hairdresser, as well as the risk to consumers of hair dyes. Although some earlier studies suggested an overrepresentation of bladder cancer in male hairdressers, the majority of modern studies do not show an increase in relevant bladder cancer risk for professional or personal use of oxidative hair dyes. Today, there seems to be no relevant bladder cancer risk from the use of oxidative hair dyes. Such a conclusion can be derived from new toxicokinetic and metabolism investigations and is in general accordance with current epidemiological data. Human urothelial cancers, chemically induced by aromatic amines, have typical latency times often longer than 20 years. Since earlier exposures could have an impact decades later, the possibility of bladder cancer in hairdressers having intensively worked with permanent hair dyes during earlier decades (prior to the 1980s) should be taken into account.

Reconstruction of N-acetyltransferase 2 haplotypes using PHASE

The genotyping of N-acetyltransferase 2 (NAT2) by PCR/RFLP methods yields in a considerable percentage ambiguous results. To resolve this methodical problem a statistical approach was applied. PHASE v2.1.1, a statistical program for haplotype reconstruction was used to estimate haplotype pairs from NAT2 genotyping data, obtained by the analysis of seven single nucleotide polymorphisms relevant for Caucasians. In 1,011 out of 2,921 (35%) subjects the haplotype pairs were clearcut by the PCR/RFLP data only. For the majority of the data the applied method resulted in a multiplicity (2-4) of possible haplotype pairs. Haplotype reconstruction using PHASE v2.1.1 cleared this ambiguity in all cases but one, where an alternative haplotype pair was considered with a probability of 0.029. The estimation of the NAT2 haplotype is important because the assignment of the NAT2 alleles *12A, *12B, *12C or *13 to the rapid or slow NAT2 genotype has been discussed controversially. A clear assignment is indispensable in surveys of human bladder cancer caused by aromatic amine exposures. In conclusion, PHASE v2.1.1 software allowed an unambiguous haplotype reconstruction in 2,920 of 2,921 cases (>99.9%).

Induction of micronuclei in V79 cells by the anabolic doping steroids tetrahydrogestrinone and trenbolone

The synthetic steroid tetrahydrogestrinone is a new "designer drug" and was recently detected to be illegally used in sports. It is chemically closely related to trenbolone that is known as an animal growth promoter. The potencies of trenbolone, tetrahydrogestrinone and testosterone to induce micronuclei in V79 cells in vitro were determined. CREST analysis was employed to differentiate between aneugenic or clastogenic mechanisms. Cytotoxicity and an influence on the cell cycle were assessed in parallel. Incubations with testosterone, at concentrations between 3 and 300 microM, failed to induce micronuclei. By contrast, tetrahydrogestrinone and trenbolone increased the rate of micronuclei significantly, up to a doubling of the micronuclei rate of untreated controls. Tetrahydrogestrinone and trenbolone displayed a bell-shaped dose-response curve, with maximal effects observed at 3 and 30 microM, respectively. The micronuclei induced by tetrahydrogestrinone and trenbolone were predominantly kinetochor (CREST) positive, pointing to an aneugenic mode of action. This may be related to the specific structure of both molecules with a system of activated double bonds. As the genotoxic effect of tetrahydrogestrinone at a chromosomal level appears at a low concentration range, it cannot be ruled out that tetrahydrogestrinone presents a genotoxic hazard on a chromosomal level under conditions of its current misuse in sports.

Acrylamide exposure via the diet: influence of fasting on urinary mercapturic acid metabolite excretion in humans

Acrylamide (AA) is carcinogenic in animals and classified by the International Agency for Research on Cancer as probably carcinogenic in humans. Regarding the AA contents of food the diet significantly contributes to the overall AA burden of the general population. However, it is unclear to which degree the diet, apart from smoking, contributes to the internal AA exposure. Therefore the influence of an AA-free diet on the excretion of urinary mercapturic acid metabolites derived from AA in three healthy volunteers fasting for 48 h was examined. Urinary AA mercapturic acid metabolites were considerably reduced after 48 h of fasting. The levels were even well below the median level in non-smokers. This confirms that the diet is the main source of environmental AA exposure in humans, apart from smoking. Other possible AA sources could be of minor quantitative importance only.

Simultaneous determination of daidzein, equol, genistein and bisphenol A in human urine by a fast and simple method using SPE and GC-MS

Human diet contains weakly estrogenic compounds such as daidzein (DAI) and genistein (GEN), phytoestrogens present in soy and many vegetables as well as bisphenol A (BPA), a contaminant from packing materials and plastic containers for foods and beverages. In light of concerns about hormonally active agents, biomonitoring methods are needed to assess human exposure to such compounds. A method for simultaneous determination of DAI, its metabolite equol (EQ), GEN, and BPA by GC-MS analysis was established, validated and applied to measure concentrations in human urine. Sample preparation involves enzymatic conjugate cleavage, SPE and derivatization by silylation. For GC/MS analysis, deuterated DAI and GEN and( 13)C-BPA are used as internal standards. LOD are 4, 4, 5 and 3 ng/mL urine for DAI, EQ, GEN and BPA, respectively. Interassay variations were 9% for DAI, 15% for EQ, 18% for GEN and 10% for BPA. Simple workup and accuracy of the method are suited for biomonitoring. An analysis of urine samples from 15 adults consuming typical German food revealed dietary exposure to phytoestrogens in all samples: GEN concentrations ranged between 13 and 238 ng/mL, those for DAI ranged from 12 to 356 ng/mL. More than half of the individuals excreted also the more estrogenic metabolite EQ, at levels of 8-128 ng/mL. Higher concentrations (GEN: 820, DAI: 960 and EQ: 1740 ng/mL) were measured in a 24 h urine sample upon ingestion of soy protein (50 g with 12.9 mg DAI and 25.2 mg GEN). Only urine collected after some days on strict phytoestrogen-free diet had undetectable isoflavone levels. BPA was detected in 9 of 15 urine samples ranging from 3 to 11 ng/mL, and at 55 ng/mL in one sample. In conclusion, a reliable method to determine BPA and isoflavones in urine was established and applied in a pilot study: Biomonitoring results show much higher dietary exposure to phytoestrogens than to BPA in German adults.

Breast cancer: a candidate gene approach across the estrogen metabolic pathway

Polymorphisms within the estrogen metabolic pathway are prime candidates for a possible association with breast cancer risk. We investigated 11 genes encoding key proteins of this pathway for their potential contribution to breast cancer risk. Of these CYP17A1, CYP19A1, EPHX1, HSD17B1, SRD5A2, and PPARG2 participate in biosynthesis, CYP1A1, CYP1B1, COMT, GSTP1, and SOD2 in catabolism and detoxification. We performed a population-based case-control study with 688 incident breast cancer cases and 724 controls from Germany and genotyped 18 polymorphisms by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), PCR based RFLP (restriction fragment length polymorphism), and TaqMan allelic discrimination. Genotype frequencies were compared between cases and controls and odds ratios were calculated by conditional logistic regression. Further statistical analyses were based on cluster analysis, multifactor dimensionality reduction, logic regression, and global testing. Single factor analyses pointed to CYP1B1_1294_GG as a possible breast cancer risk modulator (OR = 2.57; 95% CI: 1.34-4.93) and two way stratification suggested associations between BMI > or = 30 kg/m(2) and COMT_472_GG (P = 0.0076 and P = 0.0026), BMI < 20 kg/m(2) and HSD17B1_937_GG (P = 0.0082) as well as CYP17A1_-34_CC and HRT use > or =10 years (P = 0.0063). Following correction for multiple testing none of these associations remained significant. No significant association between breast cancer risk and genetic polymorphisms was observed in multifactor analyses. The tested polymorphisms of the estrogen metabolic pathway may not play a direct role in breast cancer risk. Therefore, future association studies should be extended to other polymorphisms and other regulatory pathways.

Re-assessment of the influence of polymorphisms of phase-II metabolic enzymes on renal cell cancer risk of trichloroethylene-exposed workers

PROBLEM

Individual differences in susceptibility to trichloroethylene-induced nephrocarcinogenicity may be conferred by genetic polymorphisms of glutathione S-transferases (GST), because enzymes of this group are pivotal for the metabolic activation of trichloroethylene. Because of a potential involvement of N-acetylation in the detoxication of reactive trichloroethylene metabolite(s) to N-acetyl-cysteine derivatives, polymorphisms of the NAT2 gene may also be relevant.

METHODS

The primary collective used for a re-investigation of these questions was that of a hospital-based case-control study by Brüning et al. (Am J Ind Med 43:274-285, 2003) of 134 renal cell cancer cases (20 cases exposed to trichloroethylene) and 401 matched controls. Genetic polymorphisms of GSTT1, GSTM1, GSTP1 and NAT2 were studied. Additional control collectives of non-diseased persons were used for comparison of allele frequencies.

RESULTS

No genetic influences on the development of renal cancer due to trichloroethylene were apparent, related to the deletion polymorphisms of GSTT1 and GSTM1, as well as to the NAT2 rapid/slow acetylator states. However, renal cell cancer cases displayed a somewhat higher proportion of the homozygous GSTP1 313A wild type (GSTP1*A), although this was not statistically significant (chi(2) test: P=0.1071, when using only the original controls of Brüning et al. (2003); P=0.0781 with inclusion of the additional controls).

CONCLUSION

The re-investigation does not confirm the working hypothesis of an influence of the deletion polymorphisms of the glutathione S-transferases GSTT1 and GSTM1 on renal cell cancer development due to high occupational exposures to trichloroethylene.

Proposed criteria for specific and non-specific chromosomal genotoxicity based on hydrophobic interactions

Tests for chromosomal damage are indispensable in the genotoxicity testing battery. Thus, positive results of clastogenicity or aneugenicity tests are of key relevance in safety assessment and product development. Schultz and Onfelt [N. Schultz, A. Onfelt, Sensitivity of cytokinesis to hydrophobic interactions. Chemical induction of bi- and multi-nucleated cells, Chem. Biol. Interact. 126 (2000) 97-123.] have studied the chemical induction of bi- and multi-nucleated cells in Chinese hamster V79 cells and compared non-specific agents with inducers acting through a known specific mechanism. They separated compounds with a specific action from those with a non-specific action based on lipophilicity, following a theory of hydrophobic interactions with processes of cytokinesis. It appeared possible to broaden the original database of this concept to include aneugenic as well as clastogenic compounds studied in the micronucleus (MN) test. The datasets used for this purpose were (A) the original dataset of Schultz and Onfelt [N. Schultz, A. Onfelt, Sensitivity of cytokinesis to hydrophobic interactions. Chemical induction of bi- and multi-nucleated cells, Chem. Biol. Interact. 126 (2000) 97-123.], and two sets (B, C) of our own data from studies in V79 cells in vitro. As the particular endpoints used were different (A: counts of bi- and multi-nucleated cells, B/C: micronucleus counts) the coherence of the experimental data sets was validated by including compounds belonging to both collections. Data set B included compounds with a specific effect on the mitotic spindle (nitrobenzene and benzonitrile) and data set C included the phytoestrogens genistein and daidzein, as well as a number of hormonal steroids with unknown mode of action. Taking all three data sets (A, B, C) together, the 33 compounds investigated covered a total lipophilicity range of logP between -0.51 (diamide) and 5.65 (17alpha-propylmesterolone). In order to separate statistical outliers (with a specific mode of action to be likely) from the large cluster of compounds with non-specific genotoxicity related to hydrophobic interactions, the method of robust regression was applied. It appeared that all compounds with a specific mode of action were in fact outliers of the lipophilicity rule. Genistein, a weak clastogen causing chromosomal aberrations and being discussed to induce topoisomerase-2 mediated DNA breaks, came close to the statistical borderline between compounds with specific and non-specific chromosomal genotoxicity. A general procedure is proposed, applicable in chemical product development, to screen specific and non-specific modes of action.

Occupational exposure of hairdressers to [14C]-para-phenylenediamine-containing oxidative hair dyes: A mass balance study

We monitored the exposure of hairdressers to oxidative hair dyes for 6 working days under controlled conditions. Eighteen professional hairdressers (3/day) coloured hairdresser's training heads bearing natural human hair (hair length: approximately 30 cm) for 6 h/working day with a dark-shade oxidative hair dye containing 2% [14C]-para-phenylenediamine (PPD). Three separate phases of hair dyeing were monitored: (A) dye preparation/hair dyeing, (B) rinsing/shampooing/conditioning and (C) cutting/drying/styling. Ambient air and personal monitoring samples (vapours and particles), nasal and hand rinses were collected during all study phases. Urine (pre-exposure, quantitative samples for the 0-12, 12-24, 24-48 h periods after start of exposure) and blood samples (blank, 4, 8 or 24 h) were collected from all exposed subjects. Radioactivity was determined in all biological samples and study materials, tools and washing liquids, and a [14C]-mass balance was performed daily. No adverse events were noted during the study. Waste, equipment, gloves and coveralls contained 0.41+/-0.16%, dye mixing bowls 2.88+/-0.54%, hair wash 45.47+/-2.95%, hair+scalp 53.46+/-4.06% of the applied radioactivity, respectively. Plasma levels were below the limit of quantification (10 ng PPDeq/mL). Total urinary 0-48 h excretion of [14C] levels ranged from a total of <2-18 microg PPDeq and was similar in subjects exposed during the different phases of hair dyeing. Minimal air levels at or slightly above the limit of quantification were found in a few personal air monitoring samples during the phases of hair dyeing and hair cutting, but not during the rinsing phase. Air area monitoring samples or nasal rinses contained no measurable radioactivity. Hand residues ranged from 0.006 to 0.15 microg PPDeq/cm2, and were found predominantly after the cutting/drying phase. The mean mass balance of [14C] across the six study days was 102.50+/-2.20%. Overall, the mean, total systemic exposure of hairdressers to oxidative hair dyes during a working day including 6 hair dyeing processes was estimated to be <0.36 microg PPDeq/kg body weight/working day. Our results suggest that (a) current safety precautions for the handling of hair dyes offer sufficient protection against local and systemic exposure and (b) professional exposure to oxidative hair dyes does not pose a risk to human health.

Genotoxicity and potential carcinogenicity of 2,4,6-TNT trinitrotoluene: structural and toxicological considerations

Environmental contamination with 2,4,6-TNT (trinitrotoluene) represents a worldwide problem. Concern for carcinogenicity can be derived from chemically related compounds, especially the dinitrotoluenes. In the metabolism of TNT, the reductive routes are preponderant. The main urinary metabolites of TNT are 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene. In humans exposed to TNT, the formation of hemoglobin adducts of the amino-dinitrotoluenes is in general concordance with the ratio of urinary excretion. The variations in quantities of excreted metabolites among the different occupational cohorts studied are likely explained by the different routes of exposure to TNT, including dermal uptake. Most studies show that urinary excretion of the amino-dinitrotoluenes (4-amino-dinitrotoluene plus 2-amino-dinitrotoluene) in a range of 1 to 10 mg L(-1) (5-50 microM) are not uncommon--for instance in persons employed with the disposal of military waste. Trinitotoluene is mutagenic in Salmonella typhimurium strains TA98 and TA100, with and without exogenous metabolic activation. Mutagenic activity has been found in urine from workers who were occupationally exposed to TNT. An unpublished 2-year study was reported in 1984 by the IIT Research Institute, Chicago, IL. Fischer 344 rats were fed diets containing 0.4, 2.0, 10, or 50 mg/kg TNT per day. In the urinary bladder, hyperplasia (12 of 47 animals p < .01) and carcinoma (11 of 47 animals, p < .05) were observed at significant levels in high-dose (50 mg kg(-1)) females and in one or two females, respectively, at 10 mg kg(-1). Taking all the available evidence together, the appropriate precautions should be taken.

Cytochrome P450 interactions in human cancers: new aspects considering CYP1B1

Molecular epidemiological studies are now a powerful tool to determine differential genetic susceptibilities to cancer-causing agents, and to obtain information on potential mechanisms. Cytochrome P450 (CYP) allelic variants are considered biomarkers of susceptibility to cancer. Such variants have an influence on the bioactivation and thereby on the potency of chemical carcinogens. This is very much straight forward for tobacco smoke-related human cancers. A new aspect is the implication of CYP1B1 in tobacco smoke-related cancers at several organ sites. On this basis, the present review is focused on lung, breast, urinary bladder and head and neck cancer. The CYP profile of the human lung includes CYP1A1, -1B1, -2A6, -2A13, -2B6, -2C18, -2E1, -2F1, -3A5 and -4B1. Polycyclic aromatic hydrocarbons (PAHs) and nitrosamines, as active components of tobacco smoke, appear as primary chemical factors for lung malignancies. For human mammary cancer, the use of hormone replacement therapy (HRT) has been shown to be associated with an increase of breast cancer risk, and there seems to be a link between risks caused by HRT use and modifying polymorphisms of drug/xenobiotic enzymes. Specifically, an association of the CYP1B1*3/*3 genotype with increased breast cancer risks has been postulated. Cigarette smoking is a major cause of human urinary bladder cancer. Arylamines, PAHs and nitrosamines are locally activated within the urothelium. Important CYPs in the bladder epithelium of experimental animals and man are CYP1B1 and -4B1. Alcohol consumption and tobacco smoking are known as the major causes of head and neck cancers. Recently, it appears that a polymorphic variant CYP1B1*3/*3 relates significantly to the individual susceptibility of smokers to head and neck cancer, supporting the view that PAH are metabolically activated through CYP1B1. It appears that CYP1B1 plays a key role for the activation of carcinogens at several organ targets, with a likelihood of complex gene-environment interactions implying Phase II enzymes.

Relevance of the deletion polymorphisms of the glutathione S-transferases GSTT1 and GSTM1 in pharmacology and toxicology

Although cytosolic glutathione S-transferase (GST) enzymes occupy a key position in biological detoxification processes, two of the most relevant human isoenzymes, GSTT1-1 and GSTM1-1, are genetically deleted (non-functional alleles GSTT1*0 and GSTM1*0) in a high percentage of the human population, with major ethnic differences. The structures of the GSTT and GSTM gene areas explain the underlying genetic processes. GSTT1-1 is highly conserved during evolution and plays a major role in phase-II biotransformation of a number of drugs and industrial chemicals, e.g. cytostatic drugs, hydrocarbons and halogenated hydrocarbons. GSTM1-1 is particularly relevant in the deactivation of carcinogenic intermediates of polycyclic aromatic hydrocarbons. Several lines of evidence suggest that hGSTT1-1 and/or hGSTM1-1 play a role in the deactivation of reactive oxygen species that are likely to be involved in cellular processes of inflammation, ageing and degenerative diseases. There is cumulating evidence that combinations of the GSTM1*0 state with other genetic traits affecting the metabolism of carcinogens (CYP1A1, GSTP1) may predispose the aero-digestive tract and lung, especially in smokers, to a higher risk of cancer. The GSTM1*0 status appears also associated with a modest increase in the risk of bladder cancer, consistent with a GSTM1 interaction with carcinogenic tobacco smoke constituents. Both human GST deletions, although largely counterbalanced by overlapping substrate affinities within the GST superfamily, have consequences when the organism comes into contact with distinct man-made chemicals. This appears relevant in industrial toxicology and in drug metabolism.

Toxicological comments to the discussion about REACH

It is the ultimate goal of the intended REACH process (Registration, Evaluation and Authorization of Chemicals) of the European Union to identify substances of hazardous properties and to evaluate the risks of human and environmental exposure. During the last few months there has been a controversial discussion as to what extent in vitro studies and consideration of structure activity relationship provide sufficient information to waive repeated exposure studies. Industry as well as certain regulatory agencies or NGOs support this approach and propose that repeated dose studies may only be required beyond 100 t/a. From a toxicological point of view it has to be stressed that this discussion primarily considers the cost reduction and protection of animals, whereas protection of human health and the environment are secondary. In vitro studies only allow identification of specific hazardous properties which can be detected by the specific test system. Moreover, appropriate information on the dose response of adverse effects, identification of thresholds and NOELs that are essential for risk characterization cannot be obtained from these studies. Consequently, identification of all relevant hazardous properties and endpoints of adverse effects can only be determined in the intact animal by repeated dose studies such as 28-day or 90-day studies. In the absence of such information the hazard identification is incomplete and there is no basis for appropriate risk assessment of human exposure. Thus, any waiving of repeated dose studies in animals bears the probability of unforeseen effects in case of acute or continuous human exposure. From this the undersigning European Toxicologists conclude: 1. The intention of REACH is to identify hazardous properties in order that a reliable risk assessment can be made and measures taken to deal with chemicals posing a significant risk. 2. The recent debate has centered on ways in which the well established in vivo methods for risk assessment can be bypassed. 3. The evidence that the available alternatives would support such replacement is weak. Progress to improve their value for risk assessment purposes is bound to be slow because the issues are very complex. As a group of European Toxicologists we strongly support the need for more research support in these areas, but we believe that over claims for progress is damaging their development. 4. Under the circumstances only two options are available: to reduce very substantially the estimation of hazard and risk with inevitable adverse consequences for human health and environmental protection, or to continue the existing methods until properly validated new methods are available.

Benzene and its methyl-derivatives: Derivation of maximum exposure levels in automobiles

Automobile drivers are exposed to several organic hydrocarbons. Concentrations measured in passenger compartments have been reported to range between 13 and 560 microg/m(3) for benzene, 33-258 microg/m(3) for toluene, 20-250 microg/m(3) for xylene (mixed isomers) and 3-23 microg/m(3) for trimethylbenzene (mixed isomers). These aromatic hydrocarbons are emitted from gasoline and from materials inside a car. In the present study we evaluated, whether these exposures pose a potential risk to the health of drivers. Therefore, we derived maximum exposure levels inside cars for chronic (ELIA(chronic)) and short-term (STELIA) exposure. The lowest ELIA's(chronic) for benzene, toluene, xylene and trimethylbenzene were 0.083, 1.2, 8.8 and 0.31 mg/m(3), respectively. The respective STELIA's were 16, 30, 29 and 25 mg/m(3). Obviously concentrations of toluene, xylene and trimethylbenzene inside cars do not exceed their individual STELIA's. In contrast, benzene seems to be problematic, since concentrations inside cars amount up to 0.56 mg/m(3), which exceeds the ELIA(chronic) derived for benzene. This should not be underestimated, since benzene is a genotoxic carcinogen that probably acts by non-threshold mechanisms. In conclusion, concentrations of toluene, xylene and trimethylbenzene usually observed inside cars are unlikely to pose a risk to the health of drivers. A systematic toxicological evaluation of the risk associated with benzene exposure in cars seems to be necessary.

Expression of cytochrome P450 enzymes CYP1A1, CYP1B1, CYP2E1 and CYP4B1 in cultured transitional cells from specimens of the human urinary tract and from urinary sediments

Expression of cytochromes P450 CYP1A1, CYP1B1, CYP2E1 and CYP4B1 was analysed on the transcript level in human urothelial cells obtained by various methods. As a source of urothelial cells, exfoliated cells in urine samples were used. Their expression profiles were determined either immediately after centrifugal enrichment (n=4) or after their cultivation and propagation (n=8). Another source of urothelial cells were ureter specimens from surgical subjects (n=4). Generally, expression was most prominent for CYP1B1 and CYP4B1 among the CYP transcripts analysed. CYP1B1 mRNA was detected in all samples investigated except for one ureter specimen. CYP4B1 mRNA was present in cell cultures from three out of eight healthy subjects, in three out of four directly investigated urinary sediments and in the cells of all five ureter specimens of four donors investigated after resection and subsequent cell culture. In most cases, CYP2E1 transcript levels were lower than those of CYP1B1 and CYP4B1. CYP2E1 mRNA was detected in cell cultures of six out of eight healthy subjects, in one out of four urinary sediments and in three out of five ureter specimens. CYP1A1 mRNA was clearly observed only in cells from resected ureters. In cell cultures the relative mRNA expression levels varied with subjects interindividually, intraindividually and also during the time of cell culture. The study demonstrates constitutive mRNA expressions of xenobiotic metabolising CYP enzymes in human urothelial cells obtained by different methods. In particular, transcripts of CYP1B1 and CYP4B1 are present, coding for enzymes which are active in the metabolism of polycyclic aromatic hydrocarbons and arylamines, respectively.

Biological monitoring and Biological Limit Values (BLV): the strategy of the European Union

Occupational standards concerning allowable concentrations of chemical compounds in the ambient air of workplaces have been established in several countries worldwide. With the integration of the European Union (EU), there has been a need of establishing harmonised Occupational Exposure Limits (OEL). The European Commission Directive 95/320/EC of 12 July 1995 has given the tasks to a Scientific Committee for Occupational Exposure Limits (SCOEL) to propose, based on scientific data and where appropriate, occupational limit values which may include the 8-h time-weighted average (TWA), short-term limits/excursion limits (STEL) and Biological Limit Values (BLVs). In 2000, the European Union issued a list of 62 chemical substances with Occupational Exposure Limits. Of these, 25 substances received a "skin" notation, indicating that toxicologically significant amounts may be taken up via the skin. For such substances, monitoring of concentrations in ambient air may not be sufficient, and biological monitoring strategies appear of potential importance in the medical surveillance of exposed workers. Recent progress has been made with respect to formulation of a strategy related to health-based BLVs.